Scientists recently found that the oldest and thickest Arctic ice has declined by 95 percent. Photo by Martin Fuchs/Pixabay

Every month, climate scientists make new discoveries that advance our understanding of climate change's causes and impacts. The research gives a clearer picture of the threats we already face and explores what's to come if we don't reduce emissions at a quicker pace.

Our blog series, This Month in Climate Science, offers a snapshot of the month's significant scientific literature, compiled from some of the leading peer-reviewed journals. This edition explores studies published in December 2018. (To get these updates delivered right to your inbox, sign up for our Hot Science newsletter.)

Extreme weather:

Extreme weather gets more extreme: Scientists have found that the global average number of record wet months is almost 20 percent higher now than it would be if the climate were stable. These trends are most pronounced in mid to high latitudes, including Central and Eastern United States, Northern Europe and Russia, where record wet months have increased by as much as 37 percent. Other regions, such as Central Africa, are experiencing more dry months. The study suggests that between 1980 and 2013, about one-third of all dry records would not have occurred without long-term changes in the climate.

Attribution science gets stronger: The Bulletin of the American Meteorological Society (BAMS) found that human-caused climate change made several recent events—floods in Bangladesh, China and South America; heatwaves in China and the Mediterranean; droughts in East Africa and the U.S. northern Plains—more likely. The annual report analyzed ocean heat events as well, including those off the coast of Australia, which scientists found to be “virtually impossible” without climate change.

UK hit with heatwaves: The UK Met Office released an analysis of the 2018 record-breaking summer heatwave, and found that human-induced warming made it about 30 times more likely to occur.

Impacts

Thawing permafrost threatens oil and gas: A Nature study found that 3.6 million people and 70 percent of infrastructure in the Arctic are located in areas with high potential of thawing permafrost. As a result, one-third of infrastructure and almost half of oil and gas extraction fields in the Russian Arctic could experience severe damages. Scientists note that the risk is not significantly reduced even if countries meet their emissions-reduction pledges under the Paris Agreement.

Changing snowpack threatens California’s water:Modelers assessed the impacts of climate change on melting snowpack, a major source of water for California’s reservoirs. They found that under a high emissions scenario, peak snowpack will occur a month earlier, and peak water volume will decline by almost 80 percent by the end of the century.

Rapid climate change caused the largest mass extinction: The end of the Permian Period, which was more than 250 million years ago, brought the largest mass extinction in Earth’s history— up to 96 percent of marine species and 70 percent of terrestrial species. In a new study, authors found that the trigger of the mass extinction event – volcanic greenhouse gases – is analogous to the current climatic changes from human-caused emissions. Before now, researchers hadn’t ever established a quantitative link between extinction, traits of species lost and climate.

Climate impacts to economy could offset additional warming from feedbacks: Unabated climate change will lead to economic losses, and scientists have now quantified the impacts of such losses on the climate itself. They found that as economic activity declines, it can decrease energy use and, in turn, carbon dioxide emissions from fossil fuels. This can offset the increase in emissions by positive climate feedbacks from terrestrial and marine ecosystems. That being said, the authors point out that the economic losses will have high costs to society, including our ability to adapt to climate change.

Emissions and temperature

Carbon dioxide emissions grow: The Global Carbon Project found that global carbon dioxide emissions climbed to a record 37.1 gigatonnes in 2018. Fossil fuels are largely to blame—emissions from oil, gas and coal grew 2.7 percent, rising even more quickly than in 2017, which saw a 1.6 percent increase.

California’s wildfires generated significant emissions: The U.S. Department of Interior found that emissions from the record-breaking 2018 wildfire season in California were equivalent to the amount generated by a year’s worth of electricity use in the state.

No basis for “global warming pause”: Two studies released this past month find that there is little or no statistical evidence for a “pause” or “slowdown” in warming in the early 21st century, an excuse climate skeptics have long used to dispute the evidence of human-induced warming. Scientists also found there is no statistical evidence for a divergence between climate models and observations, which had been previously cited as one potential factor in the presumed pause.

Ice and sea level rise

Sea level rise from Arctic ice loss accelerating: Scientists found that sea level rise due to the loss of Arctic land ice has greatly accelerated from 1971 to 2017, –tripling between 1986-2005 and 2006-2015. Arctic land ice, largely from Greenland and Alaska, contributes about 35 percent of global sea level rise.

Greenland ice sheet is melting more than previously thought: Researchers found that Greenland ice sheet melt has been “exceptional” over at least the last 350 years. Ice melt can be traced to industrialization in the mid-1800s, but the sheet has only recently been melting at a level outside the range of natural variability.

Arctic gets a bad report card: The National Oceanic and Atmospheric Administration released its annual Arctic Report Card, finding that the oldest and thickest Arctic ice has declined by 95 percent. This is tremendously problematic given that this ice is the most stable. An eventual ice-free Arctic can lead to runaway warming, as open ocean absorbs more sunlight.